P078B — Shift Timing Solenoid B Range/Performance

OBD2 code P078B flags a problem with the sensor and actuator circuits (shift timing solenoid b range/performance). The car is usually drivable while you plan the repair. Common culprits: faulty sensor or actuator of the affected circuit, control module driver fault, open or shorted wiring in the circuit.

powertrain (engine/transmission)

Is it safe to drive?

Short-term driving is OK In most cases the car remains drivable, possibly with reduced performance or a disabled auxiliary system. If symptoms include stalling, no-start or brake/steering warnings, treat it as urgent.

How to diagnose with an OBD scanner

Read the code and freeze frame Connect an OBD2 scanner, confirm P078B is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
Check for companion codes and TSBs Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many P0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
Inspect wiring and connectors Visually inspect the wiring harness and connectors related to the shift timing solenoid b for damage, corrosion, chafing or poor contact.
Subsystem check Compare the shift timing solenoid b live reading against a known-good reference (specification or a correlated sensor) under the conditions from the freeze frame.
Subsystem check Measure reference voltage, ground and signal continuity at the component connector.
Subsystem check Wiggle-test the harness while watching the signal in live data — dropouts reveal broken wires.
Verify the repair Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm P078B does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for P078B (parts and labor, USD, independent shop rates): Repair wiring or connectors: $80–$250; Replace the faulty sensor or actuator: $150–$500; Control module repair: $300–$1,000. Overall, fixing P078B usually costs between $80 and $1,000. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Common questions

How do I diagnose P078B myself?

Start with a scan: confirm P078B, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the shift timing solenoid b, and verify the suspect component against live data before buying parts.

Will P078B clear itself?

Sometimes P078B clears after a few drive cycles if the fault was intermittent — for example a loose connector or a tank of bad fuel. The underlying cause usually remains, so the code tends to return. Clear it once; if it comes back, diagnose rather than erase it repeatedly.

What is the most common cause of P078B?

The most common causes are: faulty sensor or actuator of the affected circuit, control module driver fault, open or shorted wiring in the circuit.

What does OBD2 code P078B mean?

How much does it cost to fix P078B?

Repair wiring or connectors — $80–$250; Replace the faulty sensor or actuator — $150–$500; Control module repair — $300–$1,000. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

When your check engine light comes on and a scan tool reveals code P078B, it's telling you that the transmission control module has detected a problem with the shift timing solenoid B circuit. Specifically, the Powertrain Control Module (PCM) is reporting a range or performance issue — the solenoid's electrical signal falls within acceptable voltage limits, but the behavior doesn't match what the computer expects given the current engine load, speed, and operating conditions. This is a category-1 code that originates in the engine/transmission management system.

The shift timing solenoid B is responsible for controlling hydraulic fluid flow to specific clutch packs or gear sets inside the automatic transmission. When the PCM commands a gear change, it energizes this solenoid to direct fluid pressure accordingly. For P078B to set, the module compares real-time solenoid operation against factory-calibrated thresholds over multiple drive cycles. If the readings drift outside those limits, the code triggers. The PCM simultaneously records a freeze frame — a snapshot of RPM, throttle position, coolant temperature, and vehicle speed at the exact moment the fault occurred. That data is invaluable during diagnosis because it tells you exactly what conditions provoked the failure.

What makes P078B tricky is that the wiring and connectors typically check out fine on a basic inspection. The problem usually lies with the solenoid itself degrading over time, a mechanical issue upstream that the solenoid accurately reports, or a calibration error following a software update or battery disconnect.

Common Symptoms of P078B

The transmission may hesitate, slip, or engage gears harshly during shifts
Fuel economy drops noticeably compared to normal driving
The Check Engine Light illuminates and typically stays on
The affected system may function intermittently or fail entirely
Limp-home mode activation is possible, restricting the vehicle to a single gear or preventing reverse engagement
In some cases, the transmission refuses to shift into higher gears

What Causes P078B?

Wear or internal failure of the shift timing solenoid B itself
A mechanical problem within the transmission that the solenoid correctly detects
Incorrect transmission calibration following a PCM software update or battery disconnect
A blown fuse feeding the solenoid control circuit
Corrosion, looseness, or physical damage at the electrical connector
An internal driver fault within the transmission control module
Open circuits, short-to-ground faults, or damaged wiring insulation in the solenoid circuit

How to Diagnose P078B

Connect an OBD2 scanner and verify that P078B is stored as a permanent code. Save the associated freeze frame data before clearing anything — that snapshot holds the operating conditions present when the fault first appeared.
Review all other stored codes alongside P078B. Related faults often expose the true root cause. Check for technical service bulletins (TSBs) specific to your make, model, and model year using your VIN on the manufacturer's website or NHTSA.gov — many transmission-related codes have documented factory remedies or calibration updates.
Perform a hands-on inspection of the wiring harness and connectors tied to the shift timing solenoid B. Look for chafed insulation, bent pins, moisture intrusion, greenish corrosion deposits, or connectors that aren't fully seated.
Compare the live data stream from the solenoid against factory specifications or a correlated sensor reading while recreating the freeze-frame conditions. Any significant deviation points toward component degradation.
With the connector disconnected, use a multimeter to verify reference voltage, proper ground integrity, and signal continuity through the circuit. Check for unwanted resistance that shouldn't be present.
Perform a wiggle test on the harness while monitoring live data. Watch the signal for drops, spikes, or complete dropout — these indicate cracked wires or loose terminals that don't show up when the car sits still.
Clear the code, complete a drive cycle that reproduces the freeze-frame conditions (specific RPM, load, temperature, and speed), and verify that P078B does not return.

Repair Options and Costs

Wiring or connector repair: $80–$250 — often as simple as cleaning terminals, applying dielectric grease, and re-securing loose clips.
Shift timing solenoid B replacement: $150–$500 — parts range from $40 to $250 depending on brand and transmission design, with 1–2 hours labor at typical independent shop rates.
Control module repair or replacement: $300–$1,000 — this is the most expensive scenario and should only be pursued after all other possibilities are eliminated.

How Much Does Fixing P078B Cost?

The total bill hinges entirely on which component is actually at fault. At an independent repair shop, wiring repairs typically run $80 to $250. If the solenoid itself is bad, expect to pay $150 to $500 for parts and labor. Control module work — whether programming, repair, or full replacement — ranges from $300 to $1,000. Most P078B cases land in the $150–$500 range. Spending time on accurate diagnosis before purchasing parts almost always saves money, because the control module replacement scenario is rarely the culprit despite being the most dramatic option.

Can You Drive with P078B?

In most instances the vehicle remains drivable, though you may notice sluggish acceleration, poor shift quality, or reduced fuel economy. If the transmission enters limp mode, power will be severely limited. Treat P078B as urgent if you experience stalling, failure to start, or warnings related to braking or steering systems. Otherwise, schedule diagnosis within a week or two to prevent secondary damage to internal transmission components.